Radiation detector and amplifier having an input axial slot



Nov. 26, 1968 c HENDEE 3,413,479

RADIATION DETECTOR AND AMPLIFIER HAVING AN INPUT AXIAL SLOT Filed July 14, 1966 2 Sheets-Sheet l Nov. 26, 1968 c. F. HENDEE RADIATIZN DETECTOR AND AMPLIFIER HAVING AN INPUT AXIAL SLOT- 2 Sheets-Sheet 2 Filed July 14, 1966 ilafAerry/lr I TOF VIK United States Patent Office 3,413,479 Patented Nov. 26, 1968 3,413,479 RADIATION DETECTOR AND AMPLIFIER HAVING AN INPUT AXIAL SLOT Charles F. Hendee, Farmington, Mich., assignor to The Bendix Corporation, a corporation of Delaware Filed July 14, 1966, Ser. No. 565,261 18 Claims. (Cl. 250207) This invention pertains to a radiation detector and amplifier and more particularly to a detector and amplifier for detecting and amplifying radiation which occurs along points on lines from devices such as spectrometers.

In applications requiring detection and amplification of lines of radiation, such as parallel lines of radiation in a diffraction pattern, it has been customary in the art to arrange a column of channel electron multipliers, of the kind disclosed in Patent No. 3,128,408 to Goodrich and Wiley entitled, Electron Multiplier, where the input ends of the column of multipliers were placed in a line to receive the line of radiation. This practice was not entirely satisfactory, primarily due to the necessity for making the gains from the channels uniform so that for a given input, all of the channels would have approximately the same output which could 'be counted or which could actuate an output circuit.

Objects of this invention include an improved device which can receive all points along a line of radiation and amplify them to a single amplified level regardless of the initial strength of the radiation or location of the radiation along the line. With this invention, only a single channel electron multiplier will detect and amplify the entire line of radiation, instead of a column of matched channels. This is accomplished by a slot lengthwise in the channel electron multiplier and operating the channel electron multiplier at saturation which is a condition of suflicient amplification to result in substantially all input pulses, regardless of position of entry, amplified to the same level. By so operating the channel, the output for all points along the slot and for all levels of input energy will be at the particular saturation level of the channel.

Feedback is more likely to occur under the above conditions of amplification. Feedback may be caused by gas molecules in the channel multiplying path which are ionized by the multiplied electrons. Under saturated conditions there are more electrons and hence the chance of ionization is greater. The ionized gas molecules being of a positive charge are accelerated in a reverse direction toward the input of the channel multiplier and if they strike the surface near the input end, they cause substantial additional feedback generated multiplication which would lead to a continuous operating condition if the feedback were not minimized. Feedback may also be due to other causes such as light generated by secondary emission and by ionization. This invention minimizes the feedback by curving the tube near the output end so that the positive ions are caused to strike the surface near the output end and multiplication due to these surface collisions will be small since there will be fewer collisions with the multiplying surface before the electrons are emitted. Since most of the ionization occurs near the output end due to the fact that the electron concentration at that area is the greatest, curving the multiplier near the output end produces desired results.

It is an object of this invention to place a plurality of the slotted channels above described so that the slots are parallel to each other and register with the output of a spectrometer to detect and amplify lines of diffraction or dispersion from the spectrometer.

It is an object of this invention to cover the end of the channel multiplier near the slot to prevent entrance of unwanted particles and to minimize end effects to the amplifier field.

It is an object to coat the walls of the slot with a conductive material to minimize potential buildup due to electrons and other particles striking the slot wall surface and causing secondary electron emission therefrom.

These and other objects will become more apparent to one skilled in the art when preferred embodiments of this invention are described in connection with the drawings in which:

FIGURE 1 is a perspective schematic view of a single slotted multiplier of this invention;

FIGURE la is an enlarged perspective partial view of the slot end of the multiplier of FIGURE 1;

FIGURE 1b is a second embodiment of this invention showing a different curvature configuration;

FIGURE 2a is an enlarged perspective view of a partial multiplier channel shown in FIGURE 1;

FIGURES 2b and 2c are graphs showing the characteristics of the tube in FIGURE 2a;

FIGURE 3 is an embodiment of this invention showing broken away evacuated tube having a coiled slotted channel therein;

FIGURE 3a is a section taken at 3a3a of the embodiment of FIGURE 3;

FIGURE 4 is a view similar to that of FIGURE 3 showing a plurality of curved channels utilized in an evacuated tube; and

FIGURE 5 is a schematic perspective showing of a plurality of curved slotted channels utilized in a spectrometer.

In FIGURES l and 1a is shown a. preferred embodiment of this invention comprising a channel electron multiplier 20 which may have a length to diameter ratio of approximately 50 to 1 and a semiconducting inner surface 21 of relatively high resistance and secondary electron emission. Suitable compositions of resistive secondary emissive material may be used and channel 20 may be of a material having a resistive characteristic throughout. A slot 24 is formed longitudinally of the input end of the multiplier tube. Slot 24 is shown with a conductive coating 26 on the faces thereof. While slot 24 is shown having parallel sides, slot configurations having non parallel sides are possible. A conductive or metallic cap 28 is shown placed over the tube at the slotted end but satisfactory operation is possible without cap 28. The purpose of cover 28 is to prevent unwanted particles from entering the end of the tube and also to minimize end effects to the electric field within the multiplying tube 20. Conductive means, for example a conductive paint 30, is placed on the tube end at the output end in the disclosed embodiment.

A battery 32 is placed across the multiplier channel 20 and supplies a voltage, such as 2500 volts, across the channel 20. This provides in the channel an electric field having field lines which are substantially parallel to the tube axis throughout the length thereof with the output end being more positive than the input end in order to accelerate electrons to the output end. A voltage such as volts is supplied by battery 34 between coating 30 and anode 36 which collects the electrons at the output end of the tube 20. A pulse detector 38 measures and records the output pulses to anode 36.

Directly opposite slot 24, the inner wall of tube is a coating 40 which may be nickel, cesium iodide, gold, or other suitable photocathode material so that the radiation 42 coming through slot 24 will be converted to electrons which are accelerated down the tube 20 and multiplied. Alternatively, the resistive coating on the tube 20 may itself be used as a photocathode.

Operation of the embodiment FIGURES l' and 1a Assume a line of radiation which may include charged and neutral particles as well as light, shown by arrows 42, to be directed at slot 24 of the tube 20. It is desired that any radiation along the line that passes through any point along slot 24 should result in signals amplified to the same level regardless of the position and of the signal along slot 24 or regardless of the energy of the incoming signal. This is so because the radiation in line 42 may be of a random nature varying in energy and with only portions of the line being radiated at any one time. Such amplification is achieved by saturating channel 20 or amplifying at a high amplification level. In this manner weak signals are amplified to the same level of amplification as high energy signals and signals passing through one end of slot 24 will receive amplification to the same level of amplification as Signals passing through the opposite end of slot 24. Hence, the detector 38 can count all signals that are received. This provides a line radiation detector with only a single channel, thereby obviating the need for matching a column of channels for line detection.

During operation, the output end of tube 20 has a very high concentration of accelerating electrons and, even though tube 20 is operated in a substantially evacuated environment, the residual gas molecules in the tube are ionized at the output end and have a positive charge due K to an electron being knocked from their orbit. The thusly formed positive ions are accelerated in a reverse direction down tube 20 but due to the curve near the output end of tube 20 they will impact against the multiplier surface before traveling very far. The secondary electrons caused by the impacting positive ions receive a very small amplification since they are formed near the output end of tube 20. Without the curvature of tube 20, the positive ions could be accelerated to points near the input end of the tube resulting in secondary emission from the tube walls that would receive large multiplication that could cause a runaway or continuous operation condition regardless of the presence of an input signal through slot 24. In this manner, the feedback effects of the positive ions are minimized.

The conductive coating 26 may be placed on the walls of slot 24 to prevent the formation of potential wells which are caused by electrons hitting the walls resulting in secondary emisston from the walls. If the walls were insulative, every time secondary emission occurred, a small positive charge would appear on the wall due to the loss of the secondary electrons. Over a period of time, this may result in a very high positive voltage on the slot walls distorting the field within the multiplier. By placing a conductive coating 26 on the walls thereof, secondary electrons which are lost are quickly resupplied by the potential source connected to the end of tube 20 which in this case is battery 32, although satisfactory operation is possible without coating 26 under certain conditions.

The embodiment of FIGURE 1b shOWs a tube 46 of similar construction to tube 20 with the major difference being that all parts of the tube have the same degree of curvature, including that portion at which slot 48 is formed.

The operation of the embodiment of FIGURE 1 at saturation current is shown in FIGURES 2a, 2b and 20. An enlarged, partial view of slotted channel 20 is shown in FIGURE 2a. A beam of light is moved from the left end of slot 24 to the right end and the output is recorded in FIGURES 2b and 20. In the graphs of FIG URES 2b and 2c, the abscissa is the distance along the slot 24 while in FIGURE 2b the ordinate is the output counting rate for pulses of the beam 25 for various positions along slot 24. In FIGURE 2c the ordinate is the average pulse strength at the output of the tube for inputs of beam 25 at various points along channel 24. It is seen that in FIGURE 2b and more noticeably in FIGURE 20, for most positions of beam 25 along slot 24, the counting rates and pulse height are substantially even. The above was obtained for a channel having a 270 curvature and with a slot which is five tenths millimeters wide and ten millimeters long.

Embodiment of FIGURE 3 In the embodiment of FIGURE 3, the tube 50 has a slot 52 formed in the end thereof and is constructed in a manner similar for that of tube 20 in FIGURE 1 but with multiplier channel 50 being coiled near the output end. A battery 54 is placed across the opposite ends of channels 50 and a resistance 56 is between the output end of the multiplier and the battery. A condenser 58 is between resistor 56 and a pulse counting circuit 60. Channel 50 is placed in an evacuated tube 62 having a photocathode surface 64 deposited on the wall thereof opposite slot 52 so that radiation falling on photocathode surface 64 will cause electron emission into slot 52.

In this embodiment, there is no collecting anode since an output pulse temporarily reduces the voltage across the tube 50 which reduction is sensed across capacitor 58 and detected by and recorded in pulse circuit 60, as is known in the art.

Embodiment of FIGURE 4 The device of FIGURE 4 is similar to that of FIGURE 3 with tubes 66 being aligned in an evacuated tube 68 and each having slots 70 therein which are in parallel alignment for reception of a diffraction pattern, as shown in FIGURE 5, or other use. Tubes 66 may be prepared in the same manner as tube 20 in FIGURE 1 and have voltage potentials placed thereacross and detecting circuits connected thereto.

Embodiment 0 FIGURE 5 In FIGURE 5 a plurality of curved channels 74 each having a slot 76 at one end thereof are in parallel alignment and may be constructed in the manner of tube 20 in FIGURE 1. Anodes 78 are located at the output of the channels 74 and are connected to pulse circuits 79. A light source 80 directs a light beam 82 to be analyzed to a diffraction grating 84, of the kind well known in the art, which diffracts the radiation 82 into a plurality of parallel lines 86. Tubes 74 have been previously arranged so that the slots 76 register with the lines 86 from diffraction grating 84. The composition of the light ray 82 can then be determined by the outputs of tubes 74 which are recorded in pulse circuits 79. Also, by placing a dispersion apparatus in place of grating 84, particles are separated according to mass or charge and the spectrum of separation can be detected and recorded by tubes 74.

Other applications of this invention would include detection of the presence of a spot of light where the spot may occur in a large range of positions along a rectilinear or curved line. The slot in the channel may be designed to conform with the path on which the spot may appear.

Although this invention may be disclosed and illustrated with reference to particular applications, the principles involved are susceptible of numerous other applications which will be apparent to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.

Having thus described my invention, I claim:

1. Apparatus comprising a channel having an input end, an output end and having a continuous secondary electron emissive resistive surface along the channel, said channel being adapted to carry a current flow resulting in an establishment of a field from the input channel end to the output channel end along the channel length, a slot being formed at the input channel end, said slot being essentially parallel to the channel axis, said slot having a dimension parallel to the channel axis which is substantially larger than the dimension which is transverse to the channel axis, for receiving radiation along a narrow beam of a width up to the length of said larger dimension of said slot.

2. The apparatus of claim 1 with voltage means connected between said input end and output end to cause a current flow in said channel surface and establish a field from the input channel end to the output channel end.

3. The apparatus of claim 1 with means for confining said channel in an evacuated environment.

4. The apparatus of claim 1 with said voltage means operating said channel at an amplification to result in a saturated condition so that all input signals that enter said slot are amplified to substantially the same level.

5. The apparatus of claim 4 with feedback suppression means to minimize feedback.

6. The apparatus of claim 5 with said feedback suppression means comprising the channel axis being non rectilinear near the output end.

7. The apparatus of claim 1 with a conductive cover being on said end near said slot to prevent entrance of unwanted particles in said channel and to minimize end efiects on the field in the channel.

8. The apparatus of claim 1 with walls of said slot being conductive and being connected to said voltage means to minimize potential well buildup.

9. The apparatus of claim 6 with said channel being circular.

10. The apparatus of claim 1 with collecting means being at the output of said channel.

'11. The apparatus of claim 1 with detecting means being connected to said collecting means.

12. The apparatus of claim 1 with the walls of said slot being substantially parallel to another.

13. The apparatus of claim 1 with at least a portion of said channel axes being coiled.

14. The apparatus of claim 1 with photocathode means being aligned with said slot to receive radiation.

15. The apparatus of claim 14 with said photocathode means being on the inside wall of the channel opposite said slot.

16. Apparatus comprising radiation diffraction means for dilfracting a radiation source into a series of parallel lines,

a plurality of channel electrons multiplying tubes each having a slot longitudinally aligned near the input end thereof,

a slot in a channel being positioned to register with each of said parallel diffracted lines,

collector means being at the output of each of said channel multiplifiers,

detector means being connected to said collector means to indicate presence of a line of radiation.

17. Apparatus comprising spectrometer means for dispersing a source into a series of parallel lines,

a plurality of channel electron multiplying tubes each having a slot longitudinally aligned near the input end thereof,

a slot in a channel being positioned to register with each of said parallel dispersed lines,

collector means being at the output of each of said channel multipliers,

detector means being connected to said collector means to indicate presence of an input line.

18. The combination of claim 1 further including means for operating said channel at saturation for amplifying radiation received at any point through said slot to substantially a constant level.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,413,479 November 26, 1968 Charles F. Hendee It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 12, cancel "the"; line 36, "their should read its line 54, emisston should read emission Column 4, line 18, "channels" should read channel line 64, "may be" should read has been Column 5, lines 15 and 28, the reference numeral 1", each occurrence, should read 2 line 35, the reference numeral 1" should read l0 line 38, before "another insert one Column 6, line 7, "electrons" should read electron Signed and sealed this 14th day of April 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer 

1. APPARATUS COMPRISING A CHANNEL HAVING AN INPUT END, AN OUTPUT END AND HAVING A CONTINUOUS SECONDARY ELECTRON EMISSIVE RESISTIVE SURFACE ALONG THE CHANNEL, SAID CHANNEL BEING ADAPTED TO CARRY A CURRENT FLOW RESULTING IN AN EXTABLISHMENT OF A FIELD FROM THE INPUT CHANNEL END TO THE OUTPUT CHANNEL END ALONG THE CHANNEL LENGTH, A SLOT BEING FORMED AT THE INPUT CHANNEL END, SAID SLOT BEING ESSENTIALLY PARALLEL TO THE CHANNEL AXIS, SAID SLOT HAVING A DIMENSION PARALLEL TO THE CHANNEL AXIS WHICH IS SUBSTANTIALLY LARGER THAN THE DIMENSION WHICH IS TRANSVERSE TO THE CHANNEL AXIS, FOR RECEIVING RADIATION ALONG A NARROW BEAM OF A WIDTH UP TO THE LENGTH OF SAID LARGER DIMENSION OF SAID SLOT. 